Optical adhesive sheet

Abstract

To provide an optical adhesive sheet suitable to a use for a flexible device.SOLUTION: An optical adhesive sheet includes a base polymer and an oligomer. The oligomer is a polymer of a monomer component containing a (meth)acrylate monomer. The monomer component further includes an acidic group-containing monomer. In the optical adhesive sheet, a shear storage modulus is 350 kPa or less at -30°C. Furthermore, 8.0≤F1 is satisfied by an adhesive force F1 (N / 20 mm) to glass at a first peeling test.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical pressure-sensitive adhesive sheet. [Background technology]

[0002] A display panel has a laminated structure including, for example, a pixel panel, a polarizing film, a touch panel, a cover film, etc. In such a display panel, for example, a transparent adhesive sheet (optical adhesive sheet) is used to bond each layer in the laminated structure.

[0003] Furthermore, in recent years, development of repeatedly foldable display panels for smartphones and tablet devices has progressed. Furthermore, development of rollable display panels has also progressed. In such flexible devices such as foldable display panels and rollable display panels, each layer in the laminate structure is made to be repeatedly foldable. In flexible devices, optical adhesive sheets are used to bond each layer together (see, for example, Patent Document 1 below). The optical adhesive sheet for flexible devices described in Patent Document 1 has excellent flexibility so as to be able to withstand repeated bending, and also has excellent adhesiveness to adherends. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-122140 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, optical adhesive sheets for flexible devices are required to have excellent flexibility and even better adhesiveness. Specifically, at the folding points of a foldable display panel, a relatively large shear force is applied in the direction along the adherend, which makes the optical adhesive sheet prone to peeling. Furthermore, in the rolled state of a rollable display panel, the optical adhesive sheet is prone to peeling due to continuous shear force in the direction along the adherend. In other words, optical adhesive sheets for such applications are desired to have improved adhesiveness to the adherend.

[0006] The present invention provides an optical pressure-sensitive adhesive sheet that is suitable for flexible device applications, has excellent flexibility, and has excellent adhesiveness. [Means for solving the problem]

[0007] The present invention [1] is an optical adhesive sheet comprising a base polymer and an oligomer, wherein the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, and the monomer component further contains an acidic group-containing monomer, and the optical adhesive sheet has a shear storage modulus of 350 kPa or less at -30°C, and an adhesive strength F1 (N / 20 mm) to glass in the first peel test described below satisfies the following formula (1). 8.0≦F1 (1) (First peel test) A polyethylene terephthalate film is attached to one side of the optical adhesive sheet, and the other side is attached to a glass plate, followed by heating and pressure treatment to prepare a measurement sample. The measurement sample is left standing at room temperature for 30 minutes, and then a test piece (the polyethylene terephthalate film with the optical adhesive sheet) is peeled from the glass plate. The measurement conditions are a temperature of 25°C, a relative humidity of 55%, a peel angle of 180°, a pulling speed of 300 mm / min, and a peel length of 50 mm.

[0008] The present invention [2] includes the optical pressure-sensitive adhesive sheet according to the above [1], in which the adhesive strength F2 (N / 20 mm) to glass in the second peel test described below satisfies the following formula (2). 6.0≦F2 (2) (Second peel test) The measurement conditions are the same as those for the first peel test, except that the pulling speed is 60 mm / min.

[0009] The present invention [3] includes the optical pressure-sensitive adhesive sheet according to the above [1] or [2], wherein the (meth)acrylic acid ester monomer further includes an alicyclic alkyl group-containing (meth)acrylic acid ester monomer.

[0010] The present invention [4] includes the optical adhesive sheet according to any one of the above [1] to [3], wherein the acidic group in the acidic group-containing monomer is a carboxy group and / or a phenolic hydroxy group.

[0011] The present invention [5] includes the optical adhesive sheet according to any one of the above [1] to [4], wherein the glass transition temperature of the homopolymer of the acidic group-containing monomer is 40°C or higher.

[0012] The present invention [6] includes an optical adhesive sheet described in any one of [1] to [5] above, wherein the content of the acidic group-containing monomer in the monomer component is 1 mass% or more and 20 mass% or less.

[0013] The present invention [7] includes an optical adhesive sheet described in any one of [1] to [6] above, in which the amount of the oligomer blended per 100 parts by mass of the base polymer is 0.3 parts by mass or more and less than 1.5 parts by mass.

[0014] The present invention [8] includes the optical pressure-sensitive adhesive sheet according to any one of the above [1] to [7], which has a haze of 1% or less. [Effects of the Invention]

[0015] As described above, the optical adhesive sheet of the present invention has a shear storage modulus of 350 kPa or less at -30°C. Such an optical adhesive sheet has excellent flexibility and can relieve stresses that occur in the optical adhesive sheet and adherend upon deformation (stress relaxation). Stress relaxation in the optical adhesive sheet can ensure the conformability of the optical adhesive sheet to the adherend, and stress relaxation in the adherend can suppress damage such as cracking of the adherend.

[0016] Furthermore, in the optical pressure-sensitive adhesive sheet of the present invention, as described above, the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, and the monomer component further contains an acidic group-containing monomer, and the adhesive strength F1 (N / 20 mm) to glass in the first peel test satisfies 8.0≦F1. In other words, the adhesive strength is excellent. The excellent adhesive strength of the optical pressure-sensitive adhesive sheet can prevent the optical pressure-sensitive adhesive sheet from peeling off from an adherend that is repeatedly deformed.

[0017] The optical pressure-sensitive adhesive sheet described above is suitable for use in flexible devices. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional schematic view of one embodiment of the optical pressure-sensitive adhesive sheet of the present invention. [Figure 2] 2A shows an example of a method for using the optical pressure-sensitive adhesive sheet of the present invention, in which Fig. 2A shows a step of attaching the optical pressure-sensitive adhesive sheet to a first adherend, Fig. 2B shows a step of joining the first adherend and a second adherend via the optical pressure-sensitive adhesive sheet, and Fig. 2C shows an aging step. DETAILED DESCRIPTION OF THE INVENTION

[0019] One embodiment of the optical pressure-sensitive adhesive sheet of the present invention will be described with reference to FIG.

[0020] The optical adhesive sheet 10 has a sheet shape with a predetermined thickness and extends in a direction (plane direction) perpendicular to the thickness direction. The optical adhesive sheet 10 has a first adhesive surface 11 and a second adhesive surface 12 opposite to the first adhesive surface 11.

[0021] 1 exemplarily shows a state in which release liners L1 and L2 are bonded to a first adhesive surface 11 and a second adhesive surface 12 of an optical adhesive sheet 10. The first release liner L1 is disposed on the first adhesive surface 11. The second release liner L2 is disposed on the second adhesive surface 12.

[0022] The optical adhesive sheet 10 is an optically transparent adhesive sheet that is placed at a light passage location of a flexible device. Examples of flexible devices include flexible display panels. Examples of flexible display panels include foldable display panels and rollable display panels. Flexible display panels have a laminated structure that includes, for example, a pixel panel, a polarizing film, a touch panel, and a cover film. The optical adhesive sheet 10 is used, for example, to bond the layers in the laminated structure of a flexible display panel. The release liners L1 and L2 are each peeled off at a predetermined timing when the optical adhesive sheet 10 is used.

[0023] The optical adhesive sheet 10 is formed from a pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition includes a base polymer and an oligomer. That is, the optical adhesive sheet 10 includes a base polymer and an oligomer. The oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, and the monomer component further includes an acidic group-containing monomer. The optical adhesive sheet 10 also has a shear storage modulus at -30°C of 350 kPa or less. Furthermore, the optical adhesive sheet 10 has an adhesive strength F1 (N / 20 mm) to glass in a first peel test described below that satisfies the following formula (1):

[0024] 8.0≦F1 (1)

[0025] As described above, the optical adhesive sheet 10 has a shear storage modulus of 350 kPa or less at -30°C. Such an optical adhesive sheet has excellent flexibility and can relieve stresses that occur in the optical adhesive sheet and the adherend when deformed (stress relaxation). Stress relaxation in the optical adhesive sheet ensures the conformability of the optical adhesive sheet to the adherend, and stress relaxation in the adherend can prevent damage such as cracking of the adherend.

[0026] Furthermore, in the optical adhesive sheet 10, as described above, the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, and the monomer component contains an acidic group-containing monomer, and the adhesive strength F1 (N / 20 mm) to glass in the first peel test satisfies 8.0≦F1. In other words, the adhesive strength is excellent. The excellent adhesive strength of the optical adhesive sheet can prevent the optical adhesive sheet from peeling off from an adherend that is repeatedly deformed.

[0027] The optical adhesive sheet 10 as described above is suitable for flexible device applications. That is, the optical adhesive sheet 10 is suitable for achieving good repeated deformation of a flexible device in which the optical adhesive sheet 10 is used.

[0028] The shear storage modulus of the optical adhesive sheet 10 at -30°C is 350 kPa or less, preferably 330 kPa or less, more preferably 310 kPa or less, and even more preferably 300 kPa or less, from the viewpoint of stress relaxation during deformation (bending, curvature, etc.) of the optical adhesive sheet 10. Also, from the viewpoint of ensuring the cohesive strength of the optical adhesive sheet 10 in the low temperature range, it is, for example, 150 kPa or more, preferably 200 kPa or more, and more preferably 250 kPa or more. The shear storage modulus is determined by dynamic viscoelasticity measurement, and specific details are described in the Examples below. Methods for adjusting the shear storage modulus of the optical adhesive sheet 10 include, for example, selecting the type and adjusting the amount of the base polymer, oligomer, and crosslinking agent, and adjusting the molecular weight of the base polymer and oligomer.

[0029] From the viewpoint of improving the adhesiveness of the optical adhesive sheet 10, the glass transition temperature (Tg) of the oligomer is, for example, 50°C or higher, preferably 60°C or higher, more preferably 65°C or higher, even more preferably 100°C or higher, particularly preferably 120°C or higher, and for example, 160°C or lower, preferably 150°C or lower, more preferably 140°C or lower, even more preferably 135°C or lower. The Tg of the oligomer is preferably higher than the Tg of the base polymer. Methods for adjusting the Tg of the oligomer include adjusting the monomer composition of the oligomer and adjusting the molecular weight.

[0030] The Tg of an oligomer is the glass transition temperature (theoretical value) calculated based on the Fox equation below. The Fox equation is a relational expression between the glass transition temperature Tg of a polymer (oligomer) and the glass transition temperature Tgi of a homopolymer of the monomers constituting the polymer (oligomer). In the Fox equation below, Tg represents the glass transition temperature (°C) of the polymer (oligomer), Wi represents the weight fraction of the monomer mi constituting the polymer (oligomer), and Tgi represents the glass transition temperature (°C) of the homopolymer formed from the monomer mi. Literature values ​​can be used for the glass transition temperature of homopolymers. For example, the "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) lists the glass transition temperatures of various homopolymers. Meanwhile, the glass transition temperature of a homopolymer of a monomer can also be calculated by the method specifically described in JP 2007-51271 A.

[0031] Fox formula 1 / (273+Tg)=Σ[Wi / (273+Tgi)]

[0032] In the first peel test described below, the adhesive strength F1 (adhesion strength at 300 mm / min) of the optical adhesive sheet 10 to glass is 8.0 N / 20 mm or more, preferably 8.5 N / 20 mm or more, more preferably 8.8 N / 20 mm or more, even more preferably 9.0 N / 20 mm or more, particularly preferably 9.2 N / 20 mm or more, from the viewpoint of suppressing peeling of the optical adhesive sheet 10 from the adherend. It is also, for example, 15 N / 20 mm or less, preferably 13 N / 20 mm or less, more preferably 11 N / 20 mm or less. Methods for adjusting the adhesive strength F1 of the optical adhesive sheet 10 to glass include, for example, selecting the type of base polymer in the optical adhesive sheet 10, adjusting the molecular weight, and adjusting the blending amount. Note that selecting the type of base polymer includes adjusting the composition of the monomers that form the base polymer. Other methods include, for example, selecting the type of components other than the base polymer in the optical adhesive sheet 10 and adjusting the blending amount of these components. Components other than the base polymer include a crosslinking agent, a silane coupling agent, and an oligomer. The method for adjusting the adhesive strength F1 of the optical adhesive sheet 10 to glass is also similar to the method for adjusting the adhesive strength of the optical adhesive sheet 10 to glass in other peel tests described below.

[0033] (First peel test) A measurement sample is prepared by laminating one side of the optical adhesive sheet 10 to a polyethylene terephthalate film, laminating the other side to a glass plate, and then heating and pressurizing. The measurement sample is left to stand at room temperature for 30 minutes, and then the test piece (the polyethylene terephthalate film with the optical adhesive sheet) is peeled from the glass plate. The measurement conditions are a temperature of 25°C, a relative humidity of 55%, a peel angle of 180°, a tensile speed of 300 mm / min, and a peel length of 50 mm.

[0034] Details of the first peel test and the method for measuring the adhesive strength F1 (initial adhesive strength) of the optical adhesive sheet 10 to glass in the first peel test are specifically described in the examples described below (the same applies to the other peel tests described below and the adhesive strength of the optical adhesive sheet 10 to glass in other peel tests).

[0035] In the second peel test described below, the adhesive strength F2 (adhesion strength at 60 mm / min) of the optical adhesive sheet 10 to glass is, from the viewpoint of suppressing peeling of the optical adhesive sheet 10 from the substrate, for example, 5.0 N / 20 mm or more, preferably 6.0 N / 20 mm or more, more preferably 6.5 N / 20 mm or more, even more preferably 6.8 N / 20 mm or more, particularly preferably 7.0 N / 20 mm or more, and also, for example, 12 N / 20 mm or less, preferably 10 N / 20 mm or less, more preferably 9.0 N / 20 mm or less, even more preferably 8.0 N / 20 mm or less.

[0036] (Second peel test) The measurement conditions are the same as those of the first peel test, except that the pulling speed is 60 mm / min.

[0037] The ratio (F2 / F1) of the adhesive strength F2 to the adhesive strength F1 is, from the viewpoint of ensuring stable adhesive strength in the optical adhesive sheet 10, for example, 0.5 or more, preferably 0.6 or more, more preferably 0.65 or more, even more preferably 0.7 or more, and for example, 1.2 or less, preferably 1.0 or less, more preferably 0.9 or less, even more preferably 0.8 or less.

[0038] The difference ΔH (= ΔH2 - ΔH1) between the hydrogen bond term ΔH1 of the HSP of the base polymer and the hydrogen bond term ΔH2 of the HSP of the oligomer is, for example, 0.15 or more, preferably 0.4 or more, more preferably 0.6 or more, and even more preferably 0.8 or more, from the viewpoint of appropriately reducing the compatibility between the base polymer and the oligomer and sufficiently unevenly distributing the oligomer on and near the adhesive surfaces 11, 12. Also, from the viewpoint of preventing the compatibility between the base polymer and the oligomer from becoming too low, it is, for example, 1.3 or less, preferably 1.2 or less, and more preferably 1.1 or less. By ensuring the compatibility between the base polymer and the oligomer, the haze can be reduced in the optical adhesive sheet 10. Examples of methods for adjusting the ΔH1 of the base polymer include adjusting the monomer composition of the base polymer. Examples of methods for adjusting the ΔH2 of the oligomer include adjusting the monomer composition of the oligomer.

[0039] Here, HSP represents the Hansen solubility parameter, and δH is the hydrogen bond term in the Hansen solubility parameter that represents the energy derived from the hydrogen bonding force between molecules.

[0040] The δH of a polymer can be calculated from the mole fraction of the monomers forming the polymer and the hydrogen bond term of the monomer. The δH of an oligomer can be calculated in a similar manner. The hydrogen bond term of the monomer can be calculated, for example, using computer software HSPiP (Hansen Solubility Parameters in Practice). The method for calculating δH will be specifically described in the Examples below.

[0041] The haze of the optical adhesive sheet 10 is, for example, 1% or less, preferably 0.8% or less, more preferably 0.5% or less, and for example, 0.01% or more. The haze of the optical adhesive sheet 10 can be measured using a haze meter in accordance with JIS K7136 (2000).

[0042] The total light transmittance of the optical adhesive sheet 10 is, for example, 60% or more, preferably 80% or more, more preferably 85% or more, and for example, 100% or less. The total light transmittance of the optical adhesive sheet 10 can be measured in accordance with JIS K 7375 (2008).

[0043] The gel fraction of the optical adhesive sheet 10 is, from the viewpoint of ensuring the cohesive strength of the optical adhesive sheet 10 in high temperature regions, for example, 60% by mass or more, preferably 70% by mass or more, more preferably 75% by mass or more, and from the viewpoint of ensuring the flexibility of the optical adhesive sheet 10, for example, 90% by mass or less, preferably 85% by mass or less, more preferably 83% by mass or less, and even more preferably 82% by mass or less. Methods for adjusting the gel fraction of the optical adhesive sheet 10 include, for example, selecting the type of base polymer in the optical adhesive sheet 10, adjusting the molecular weight, and adjusting the amount blended. Methods for adjusting the gel fraction also include selecting the type of crosslinking agent and adjusting the amount blended. Specific methods for measuring the gel fraction are described in the Examples below.

[0044] <Base polymer> The base polymer is the adhesive component of the optical adhesive sheet 10. Examples of base polymers include acrylic polymers, silicone polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyvinyl ether polymers, vinyl acetate / vinyl chloride copolymers, modified polyolefin polymers, epoxy polymers, fluoropolymers, and rubber polymers. Acrylic polymers are preferred from the viewpoint of ensuring good transparency and adhesiveness. The base polymers may be used alone or in combination of two or more.

[0045] An acrylic polymer is a polymer of a monomer component (first monomer component) containing 50% by mass or more of a (meth)acrylic acid ester monomer. Note that "(meth)acrylic" refers to acrylic and / or methacrylic.

[0046] Examples of the (meth)acrylic acid ester monomer include a (meth)acrylic acid ester monomer having an alkyl group having 1 to 20 carbon atoms (an alkyl group-containing (meth)acrylic acid ester monomer) and a (meth)acrylic acid ester monomer having a hydroxy group (a hydroxy group-containing (meth)acrylic acid ester monomer). Examples of the alkyl group-containing (meth)acrylic acid ester monomer include a (meth)acrylic acid ester monomer having a chain alkyl group (a chain alkyl group-containing (meth)acrylic acid ester monomer) and a (meth)acrylic acid ester monomer having an alicyclic alkyl group (an alicyclic alkyl group-containing (meth)acrylic acid ester monomer).

[0047] Examples of the chain alkyl group-containing (meth)acrylic acid ester monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, n-hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and lauryl (meth)acrylate.

[0048] Examples of the alicyclic alkyl group-containing (meth)acrylic acid ester monomer include the alicyclic alkyl group-containing (meth)acrylic acid ester monomer in the second monomer component described below.

[0049] In order to achieve a balance between the flexibility and adhesive strength required for an optical adhesive sheet for flexible devices, the alkyl group-containing (meth)acrylic acid ester monomer in the optical adhesive sheet 10 is preferably at least one selected from first alkyl group-containing (meth)acrylic acid ester monomers having an alkyl group of 8 to 12 carbon atoms and at least one selected from second alkyl group-containing (meth)acrylic acid ester monomers having an alkyl group of 1 to 4 carbon atoms. The first alkyl group-containing (meth)acrylic acid ester monomer is preferably n-octyl acrylate (NOAA). The second alkyl group-containing (meth)acrylic acid ester monomer is preferably n-butyl acrylate (BA). More preferably, NOAA and BA are used in combination.

[0050] The content of the alkyl group-containing (meth)acrylic acid ester monomer in the first monomer component is, for example, 80% by mass or more, preferably 85% by mass or more, more preferably 88% by mass or more, and for example, less than 100% by mass, preferably 99% by mass or less, from the viewpoint of balancing flexibility and adhesive strength in the optical adhesive sheet 10. When the first alkyl group-containing (meth)acrylic acid ester monomer and the second alkyl group-containing (meth)acrylic acid ester monomer are used in combination, the content of the first alkyl group-containing (meth)acrylic acid ester monomer in the monomer component is, for example, 60% by mass or more, preferably 65% ​​by mass or more, more preferably 68% by mass or more, and for example, 85% by mass or less, preferably 80% by mass or less, more preferably 75% by mass or less. The content of the second alkyl group-containing (meth)acrylic acid ester monomer in the monomer components is, for example, 10% by mass or more, preferably 15% by mass or more, more preferably 18% by mass or more, and for example, 35% by mass or less, preferably 30% by mass or less, more preferably 25% by mass or less.

[0051] Examples of hydroxy group-containing (meth)acrylic acid ester monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. 4-hydroxybutyl acrylate (4HBA) is preferred.

[0052] The content ratio of the hydroxy group-containing (meth)acrylic acid ester monomer in the first monomer component is, for example, 1 mass% or more, preferably 3 mass% or more, more preferably 5 mass% or more, from the viewpoint of introducing a crosslinked structure into the acrylic polymer and ensuring cohesive strength in the optical adhesive sheet 10, and, from the viewpoint of adjusting the polarity of the acrylic polymer (which is related to the compatibility between various additive components in the optical adhesive sheet 10 and the acrylic polymer), is, for example, 15 mass% or less, preferably 12 mass% or less, more preferably 10 mass% or less.

[0053] The first monomer component may also contain a copolymerizable monomer copolymerizable with the (meth)acrylic acid ester monomer. Examples of the copolymerizable monomer include a monomer having a polar group. Examples of the polar group-containing monomer include a hydroxy group-containing monomer (excluding hydroxy group-containing (meth)acrylic acid ester monomers), a monomer having a nitrogen atom-containing ring, and an acidic group-containing monomer. Preferably, a monomer having a nitrogen atom-containing ring is used. In the first monomer component, the polar group-containing monomer can modify the acrylic polymer, for example, by introducing crosslinking points into the acrylic polymer or ensuring the cohesive strength of the acrylic polymer. The copolymerizable monomer may be used alone or in combination of two or more types.

[0054] Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, 4-acryloylmorpholine, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, and N-vinylisothiazole.Preferably, N-vinyl-2-pyrrolidone (NVP) is used.

[0055] When a monomer having a nitrogen atom-containing ring is used, the content ratio of the monomer having a nitrogen atom-containing ring in the first monomer component is, for example, 0.5 mass% or more, preferably 1 mass% or more, more preferably 1.5 mass% or more, from the viewpoint of ensuring the cohesive strength of the optical adhesive sheet 10 and ensuring the adhesion strength of the optical adhesive sheet 10 to the substrate, and is, for example, 10 mass% or less, preferably 5 mass% or less, more preferably 3 mass% or less, from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (which is related to the compatibility between various additive components in the optical adhesive sheet 10 and the acrylic polymer).

[0056] Examples of the acidic group-containing monomer include the acidic group-containing monomers in the second monomer component described below.

[0057] The first monomer component may contain other copolymerizable monomers in addition to those mentioned above. Examples of the other copolymerizable monomers include epoxy group-containing monomers, cyano group-containing monomers, alkoxy group-containing monomers, and aromatic vinyl compounds. The other copolymerizable monomers may be used alone or in combination of two or more.

[0058] The first monomer component preferably contains a first alkyl group-containing (meth)acrylic acid ester monomer having an alkyl group of 8 to 12 carbon atoms, a second alkyl group-containing (meth)acrylic acid ester monomer having an alkyl group of 1 to 4 carbon atoms, a hydroxy group-containing (meth)acrylic acid ester monomer, and a monomer having a nitrogen atom-containing ring. More preferably, it contains NOAA, BA, 4HBA, and NVP.

[0059] The base polymer preferably has a crosslinked structure. Methods for introducing a crosslinked structure into the base polymer include, for example, a first method and a second method. In the first method, a base polymer having a functional group reactive with the crosslinking agent and a crosslinking agent are blended into an adhesive composition, and the base polymer and the crosslinking agent are reacted in an optical adhesive sheet. In the second method, a first monomer component forming the base polymer contains a multifunctional compound as a crosslinking agent, and polymerization of the first monomer component forms a base polymer in which a branched structure (crosslinked structure) is introduced into the polymer chain. These methods may be used in combination.

[0060] Examples of the crosslinking agent used in the first method include compounds that react with functional groups (such as hydroxyl groups and carboxyl groups) contained in the base polymer. Examples of the crosslinking agent include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, and carbodiimide crosslinking agents. Isocyanate crosslinking agents are preferred because they have high reactivity with the hydroxyl groups and carboxyl groups in the base polymer and facilitate the introduction of crosslinked structures. The crosslinking agents may be used alone or in combination of two or more.

[0061] In the first method, the amount of crosslinking agent per 100 parts by mass of base polymer is, from the viewpoint of ensuring the cohesive strength of the optical adhesive sheet 10, for example, 0.01 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and from the viewpoint of ensuring good tackiness in the optical adhesive sheet 10, for example, 5 parts by mass or less, preferably 1 part by mass or less, more preferably 0.2 parts by mass or less.

[0062] In the second method, the first monomer component (including a polyfunctional compound and a monofunctional monomer for introducing a crosslinked structure) may be polymerized in one step or in multiple steps. In the multi-step polymerization method, first, a monofunctional monomer for forming a base polymer is polymerized (prepolymerization), thereby preparing a prepolymer composition containing a partial polymer (a mixture of a low-polymerization polymer and unreacted monofunctional monomer). Next, a polyfunctional compound is added to the prepolymer composition, and the mixture containing the partial polymer and the polyfunctional compound is polymerized (main polymerization). In the main polymerization, a pre-prepared oligomer (described below) can also be blended with the mixture containing the partial polymer and the polyfunctional compound. A silane coupling agent (described below) can also be blended with the mixture.

[0063] Examples of polyfunctional compounds include polyfunctional monomers and polyfunctional oligomers containing two or more ethylenically unsaturated double bonds in one molecule, and polyfunctional monomers include polyfunctional (meth)acrylates.

[0064] Examples of the polyfunctional (meth)acrylate include difunctional (meth)acrylate, trifunctional (meth)acrylate, and tetrafunctional or higher polyfunctional (meth)acrylate.

[0065] Examples of bifunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, ethoxylated bisphenol A diacrylate (BPAEODE), and neopentyl glycol di(meth)acrylate.

[0066] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl)isocyanurate.

[0067] Examples of tetrafunctional or higher polyfunctional (meth)acrylates include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0068] Examples of polyfunctional oligomers include urethane (meth)acrylate oligomers, polyester (meth)acrylate oligomers, polyether (meth)acrylate oligomers, polyol (meth)acrylate oligomers, epoxy (meth)acrylate oligomers, polyethylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate.

[0069] The polyfunctional compound may be used alone or in combination of two or more kinds. As the polyfunctional compound, preferably, a polyfunctional monomer is used. More preferably, a polyfunctional (meth)acrylate having tetrafunctional or more is used. Even more preferably, dipentaerythritol hexaacrylate is used.

[0070] In the second method, the amount of polyfunctional compound per 100 parts by mass of the monofunctional monomer of the first monomer component is, from the viewpoint of ensuring the cohesive strength of the optical adhesive sheet 10, for example, 0.02 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.07 parts by mass or more, and from the viewpoint of ensuring good tackiness in the optical adhesive sheet 10, for example, 3 parts by mass or less, preferably 1 part by mass or less, more preferably 0.5 parts by mass or less.

[0071] The base polymer can be formed by polymerizing the first monomer component. Examples of polymerization methods include solution polymerization, emulsion polymerization, and solventless photopolymerization (e.g., ultraviolet polymerization). Examples of solvents for solution polymerization include ethyl acetate and toluene. A chain transfer agent may be used in the polymerization. Examples of polymerization initiators include thermal polymerization initiators and photopolymerization initiators. For example, in the second method, the polymerization initiator is added first during prepolymerization and then second during main polymerization. The polymerization initiator may be used alone or in combination of two or more. The amount of the polymerization initiator per 100 parts by mass of the first monomer component is, for example, 0.03 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.07 parts by mass or more, and for example, 1 part by mass or less, preferably 0.5 parts by mass or less, and more preferably 0.3 parts by mass or less.

[0072] Examples of thermal polymerization initiators include azo polymerization initiators and peroxide polymerization initiators. Examples of azo polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid) dimethyl, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, and 2,2'-azobis(2-amidinopropane) dihydrochloride. Examples of peroxide polymerization initiators include dibenzoyl peroxide, t-butyl permaleate, and lauroyl peroxide.

[0073] Examples of photopolymerization initiators include radical photopolymerization initiators, cationic photopolymerization initiators, and anionic photopolymerization initiators. Examples of radical photopolymerization initiators include acylphosphine oxide photopolymerization initiators, acetophenone photopolymerization initiators, and benzoin ether photopolymerization initiators. Examples of acylphosphine oxide photopolymerization initiators include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. Examples of acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone.

[0074] The weight average molecular weight of the base polymer is, for example, 100,000 or more, preferably 300,000 or more, and more preferably 500,000 or more, from the viewpoint of ensuring cohesive strength in the optical adhesive sheet 10. The weight average molecular weight of the base polymer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

[0075] The Tg of the base polymer is, for example, 0° C. or lower, preferably −10° C. or lower, more preferably −20° C. or lower, and for example, −80° C. or higher. The Tg of the base polymer can be determined by the glass transition temperature (theoretical value) calculated based on the Fox formula described above.

[0076] The content of the base polymer in the optical adhesive sheet 10 is, for example, 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more, from the viewpoint of properly expressing basic properties such as adhesiveness, and, from the viewpoint of ensuring the content of other components in the optical adhesive sheet 10, is, for example, 99.9% by mass or less, preferably 99.5% by mass or less, and more preferably 99.0% by mass or less.

[0077] <Oligomer> The oligomer is a polymer of a monomer component (second monomer component) containing a (meth)acrylic acid ester monomer. The oligomer may be used alone or in combination of two or more kinds.

[0078] When two or more oligomers are used in combination, it is sufficient that at least one oligomer satisfies the specified parameters (e.g., glass transition temperature, difference ΔH (= ΔH2 - ΔH1) between the hydrogen bond term ΔH1 of the HSP of the base polymer and the hydrogen bond term ΔH2 of the HSP of the oligomer). In other words, when two or more oligomers are used in combination, oligomers that do not satisfy the specified parameters (e.g., glass transition temperature, difference ΔH (= ΔH2 - ΔH1) between the hydrogen bond term ΔH1 of the HSP of the base polymer and the hydrogen bond term ΔH2 of the HSP of the oligomer) may also be included within a range that does not impair the effects of the present invention. Preferably, all oligomers used in combination satisfy the specified parameters.

[0079] Examples of the (meth)acrylic acid ester monomer in the second monomer component include alkyl group-containing (meth)acrylic acid ester monomers. Examples of the alkyl group-containing (meth)acrylic acid ester monomer include chain alkyl group-containing (meth)acrylic acid ester monomers and alicyclic alkyl group-containing (meth)acrylic acid ester monomers. The (meth)acrylic acid ester monomer in the second monomer component preferably includes an alicyclic alkyl group-containing (meth)acrylic acid ester monomer.

[0080] Examples of the (meth)acrylic acid ester monomer containing a chain alkyl group in the second monomer component include the chain alkyl group-containing (meth)acrylic acid ester monomers described above for the first monomer component. Preferably, a (meth)acrylic acid ester monomer containing a chain alkyl group having an alkyl group of 1 to 6 carbon atoms is used. More preferably, a methacrylic acid ester monomer containing a chain alkyl group having an alkyl group of 1 to 6 carbon atoms is used. Even more preferably, methyl methacrylate (MMA) is used. MMA has a high glass transition temperature as a homopolymer and is relatively compatible with the base polymer.

[0081] When the second monomer component contains a chain alkyl group-containing (meth)acrylic acid ester monomer, the proportion of the chain alkyl group-containing (meth)acrylic acid ester monomer in the second monomer component is, from the viewpoint of ensuring a high Tg of the oligomer and adjusting the compatibility of the oligomer with the base polymer, for example, 20% by mass or more, preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, particularly preferably 47% by mass or more, and for example, 60% by mass or less, preferably 55% by mass or less, more preferably 50% by mass or less, even more preferably less than 50% by mass.

[0082] Examples of the (meth)acrylic acid ester monomer containing an alicyclic alkyl group in the second monomer component include a (meth)acrylic acid cycloalkyl ester monomer, a (meth)acrylic acid ester monomer having a bicyclic aliphatic hydrocarbon ring, and a (meth)acrylic acid ester monomer having a tricyclic or higher aliphatic hydrocarbon ring.Preferably, among the (meth)acrylic acid cycloalkyl ester monomer, the (meth)acrylic acid ester monomer having a bicyclic aliphatic hydrocarbon ring, and the (meth)acrylic acid ester monomer having a tricyclic or higher aliphatic hydrocarbon ring, a (meth)acrylic acid ester monomer containing a condensed ring (condensed ring-containing (meth)acrylic acid ester monomer) is used.

[0083] Examples of (meth)acrylic acid cycloalkyl ester monomers include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, cyclooctyl (meth)acrylate, and cyclododecyl (meth)acrylate. Examples of (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth)acrylate. Examples of (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring include dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

[0084] The alicyclic alkyl group-containing (meth)acrylic acid ester monomer in the second monomer component preferably includes a (meth)acrylic acid cycloalkyl ester monomer and a fused ring-containing (meth)acrylic acid ester monomer, more preferably cyclohexyl methacrylate (CHMA) and dicyclopentanyl methacrylate (DCPMA).

[0085] The proportion of the alicyclic alkyl group-containing (meth)acrylic acid ester monomer in the second monomer component is, from the viewpoints of compatibility with the base polymer and achieving a high Tg, for example, 30% by mass or more, preferably 40% by mass or more, and more preferably 45% by mass or more, and from the viewpoint of the polymerizability of the second monomer component, for example, less than 100% by mass, preferably 95% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, and particularly preferably less than 50% by mass.

[0086] When the second monomer component contains a chain alkyl group-containing (meth)acrylic acid ester monomer, the mass ratio of the alicyclic alkyl group-containing (meth)acrylic acid ester monomer to the chain alkyl group-containing (meth)acrylic acid ester monomer in the second monomer component is, from the viewpoint of increasing the Tg of the oligomer and adjusting the compatibility of the oligomer with the base polymer, for example, 0.6 or more, preferably 0.8 or more, and more preferably 0.9 or more, and for example, 5.0 or less, preferably 3.0 or less, and more preferably 1.5 or less.

[0087] The proportion of the alkyl group-containing (meth)acrylic acid ester monomer in the second monomer component is, from the viewpoint of increasing the Tg of the oligomer, for example, 80% by mass or more, preferably 85% by mass or more, more preferably 88% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, and from the viewpoint of the polymerizability of the second monomer component, for example, less than 100% by mass, preferably 99.5% by mass or less, more preferably 99% by mass or less, even more preferably 98% by mass or less, and particularly preferably 97% by mass or less.

[0088] The second monomer component contains an acidic group-containing monomer as a polar group-containing monomer. Examples of the acidic group-containing monomer include a carboxyl group-containing monomer, a phenolic hydroxyl group-containing monomer, a sulfonic acid group-containing monomer, and a phosphoric acid group-containing monomer. Preferred examples include a carboxyl group-containing monomer and a phenolic hydroxyl group-containing monomer. That is, in the acidic group-containing monomer, preferred examples of the acidic group include a carboxyl group and a phenolic hydroxyl group.

[0089] Examples of carboxyl group-containing monomers include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Examples of carboxyl group-containing monomers also include carboxyl group-containing (meth)acrylic acid ester monomers. Examples of carboxyl group-containing (meth)acrylic acid ester monomers include carboxyethyl (meth)acrylate and carboxypentyl (meth)acrylate. Preferred examples of carboxyl group-containing monomers include acrylic acid (AA) and methacrylic acid (MAA).

[0090] Examples of the phenolic hydroxy group-containing monomer include phenolic hydroxy group-containing (meth)acrylic acid ester monomers, such as hydroxyphenyl (meth)acrylate (HQMA: hydroquinone mono(meth)acrylate).

[0091] The proportion of the acidic group-containing monomer in the second monomer component is, from the viewpoint of ensuring the cohesive strength of the optical adhesive sheet 10 and the adhesion of the optical adhesive sheet 10 to the substrate, for example, 0.1 mass% or more, preferably 1 mass% or more, more preferably 1.5 mass% or more, even more preferably 2 mass% or more, and particularly preferably 2.5 mass% or more; and from the viewpoint of adjusting the glass transition temperature of the oligomer and avoiding the risk of corrosion of the substrate by acid, for example, 20 mass% or less, preferably 15 mass% or less, more preferably 12 mass% or less, even more preferably 10 mass% or less, and particularly preferably 8 mass% or less.

[0092] The glass transition temperature of the homopolymer of the acidic group-containing monomer is, from the viewpoint of increasing the Tg of the oligomer, for example, 40°C or higher, preferably 60°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher. The upper limit of the glass transition temperature of the homopolymer of the acidic group-containing monomer is not particularly limited, and is appropriately adjusted depending on the content of the oligomer in the pressure-sensitive adhesive composition (optical adhesive sheet 10) described below, within a range that ensures the flexibility of the pressure-sensitive adhesive composition. The upper limit of the glass transition temperature of the homopolymer of the acidic group-containing monomer is, for example, 300°C. Specifically, the glass transition temperature of the homopolymer of AA is 106°C, and the glass transition temperature of the homopolymer of MAA is 228°C.

[0093] The pKa (acid dissociation constant) of an acidic group-containing monomer is an index that quantitatively represents the acidity of the acidic group-containing monomer, and the smaller the pKa, the stronger the acidity. The pKa (acid dissociation constant) of the acidic group-containing monomer is, for example, 12 or less, preferably 10 or less, more preferably 8 or less, even more preferably 7 or less, particularly preferably 6 or less, and most preferably 5 or less. Specifically, the pKa of AA is 4.66, and the pKa of MAA is 4.25.

[0094] The second monomer component may contain a polar group-containing monomer other than the above-mentioned acid group-containing monomer. Preferably, the second monomer component does not contain a polar group-containing monomer other than the acid group-containing monomer. Examples of the polar group-containing monomer include a hydroxy group-containing monomer and a monomer having a nitrogen atom-containing ring.

[0095] The proportion of the polar group-containing monomer in the second monomer component is, for example, 10% by mass or less, preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0% by mass, from the viewpoint of ensuring adhesive strength to the substrate in the optical adhesive sheet 10 and adjusting the compatibility of the oligomer with the base polymer.

[0096] The second monomer component preferably contains an alkyl group-containing (meth)acrylic acid ester monomer and an acidic group-containing monomer. More preferably, it consists of an alkyl group-containing (meth)acrylic acid ester monomer and an acidic group-containing monomer. The alkyl group-containing (meth)acrylic acid ester monomer is preferably an alicyclic alkyl group-containing (meth)acrylic acid ester monomer used alone, or a combination of a chain alkyl group-containing (meth)acrylic acid ester monomer and an alicyclic alkyl group-containing (meth)acrylic acid ester monomer. Preferably, a combination of a chain alkyl group-containing (meth)acrylic acid ester monomer and an alicyclic alkyl group-containing (meth)acrylic acid ester monomer is used.

[0097] Specific examples of the second monomer component include a combination of CHMA and AA, a combination of DCPMA, MMA and MAA, and a combination of DCPMA, MMA and HQMA.

[0098] As described above, the oligomer can be obtained by polymerizing a monomer component (second monomer component) containing a (meth)acrylic acid ester monomer. Examples of polymerization methods include solution polymerization, emulsion polymerization, and solvent-free photopolymerization (e.g., ultraviolet polymerization). Examples of solvents used in solution polymerization include ethyl acetate and toluene. A chain transfer agent may be used in the polymerization to adjust the molecular weight. Examples of polymerization initiators include the thermal polymerization initiators and photopolymerization initiators described above. The polymerization initiators may be used alone or in combination of two or more. The amount of the polymerization initiator used is, per 100 parts by mass of the second monomer component, for example, 0.05 parts by mass or more, preferably 0.1 parts by mass or more, and for example, 1 part by mass or less, preferably 0.5 parts by mass or less.

[0099] The oligomer has a weight average molecular weight Mw of 1,000 or more and 30,000 or less. From the viewpoint of increasing adhesion on the surface (adhesive surfaces 11 and 12) of the optical adhesive sheet 10, the weight average molecular weight Mw of the oligomer is, for example, 4,300 or more, preferably 4,500 or more, more preferably 4,700 or more, and even more preferably 4,900 or more. From the viewpoint of uneven distribution of the oligomer on and near the surface of the optical adhesive sheet 10 (mobility to the surface), the weight average molecular weight Mw is, for example, 10,000 or less, preferably 8,000 or less, more preferably 6,000 or less, and even more preferably 5,800 or less. The weight average molecular weight Mw of the oligomer is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

[0100] The content of the oligomer in the pressure-sensitive adhesive composition (optical adhesive sheet 10) is, for example, 0.1 parts by mass or more, preferably 0.3 parts by mass or more, more preferably 0.4 parts by mass or more, and even more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the base polymer, from the viewpoint of sufficiently increasing the adhesive strength of the optical adhesive sheet 10. Also, from the viewpoint of ensuring the transparency of the optical adhesive sheet 10, it is, for example, less than 3 parts by mass, preferably 2 parts by mass or less, more preferably 1.5 parts by mass or less, even more preferably less than 1.5 parts by mass, particularly preferably 1.0 parts by mass or less, and most preferably 0.8 parts by mass or less. If the content of the oligomer in the optical adhesive sheet 10 is too large, the shear storage modulus at -30 ° C. in the optical adhesive sheet 10 may increase, and the flexibility may decrease.

[0101] The pressure-sensitive adhesive composition preferably contains a silane coupling agent. Examples of the silane coupling agent include an epoxy silane coupling agent. The content of the silane coupling agent in the pressure-sensitive adhesive composition is, relative to 100 parts by mass of the base polymer, for example, 0.1 parts by mass or more, preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, and for example, 5 parts by mass or less, preferably 3 parts by mass or less, more preferably 1 part by mass or less.

[0102] The PSA composition may contain other components as needed. Examples of the other components include solvents, tackifiers, plasticizers, softeners, antioxidants, fillers, colorants, UV absorbers, antioxidants, surfactants, and antistatic agents. Examples of the solvent include polymerization solvents used as needed during polymerization of the acrylic polymer, and solvents added to the polymerization reaction solution after polymerization. Specifically, ethyl acetate and toluene are used as the solvent.

[0103] The optical adhesive sheet 10 can be produced, for example, by applying the above-mentioned pressure-sensitive adhesive composition to a first release liner L1 to form a coating film, and then irradiating the coating film with ultraviolet light or drying the coating film. The optical adhesive sheet 10 may also be produced by applying the above-mentioned pressure-sensitive adhesive composition to a first release liner L1 to form a coating film, laminating a second release liner L2 on the coating film, and then irradiating the coating film between the release liners with ultraviolet light or drying the coating film.

[0104] Examples of the first release liner L1 include a release liner having a release treatment layer on the surface of the liner substrate, and a release liner made of a low-adhesion material. Examples of the liner substrate include a resin film and paper. Examples of the resin for the resin film include a polyester resin and a polycarbonate resin. Examples of polyester resins include polyethylene terephthalate (PET) and polybutylene terephthalate. The release treatment layer can be formed by treating the surface of the liner substrate with a release treatment agent. Examples of the release treatment agent include a silicone release treatment agent, a long-chain alkyl release treatment agent, and a fluorine release treatment agent. Examples of low-adhesion materials include a polyolefin resin and a fluorine-based polymer. Examples of polyolefin resins include polyethylene, polypropylene, and cycloolefin polymer (COP). Examples of fluorine-based polymers include polytetrafluoroethylene.

[0105] Examples of methods for applying the pressure-sensitive adhesive composition include roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and die coating. The drying temperature for the coating film is, for example, 50°C to 200°C. The drying time is, for example, 5 seconds to 20 minutes.

[0106] Examples of the second release liner L2 include a release liner having a release-treated layer on the surface of a liner substrate and a release liner made of a low-adhesion material. Specifically, the second release liner L2 is the same as that described above for the first release liner L1.

[0107] In this manner, an optical pressure-sensitive adhesive sheet 10 can be produced in which the pressure-sensitive adhesive surfaces 11, 12 are covered and protected by the release liners L1, L2.

[0108] A method of using the optical adhesive sheet 10 will be described with reference to FIGS. 2A to 2C.

[0109] 2A, the optical adhesive sheet 10 is attached to one surface in the thickness direction of a first member 21 (adherend). The first member 21 is, for example, part of the laminated structure of a flexible display panel. Specifically, the first member 21 can be a pixel panel, a polarizing film, a touch panel, or a cover film (the same applies to the second member 22 described below).

[0110] 2B, one surface in the thickness direction of the first member 21 is bonded to the other surface in the thickness direction of the second member 22 via the optical adhesive sheet 10 on the first member 21. The second member 22 is, for example, part of a laminated structure of a flexible display panel.

[0111] Next, as shown in FIG. 2C, the optical adhesive sheet 10 between the first member 21 and the second member 22 is aged. Aging increases the bonding strength between the optical adhesive sheet 10 and the members 21 and 22. The aging temperature is, for example, 20°C to 160°C. The aging time is, for example, 1 minute to 21 days. When autoclaving (heat and pressure treatment) is used for aging, the temperature is, for example, 30°C to 80°C, the pressure is, for example, 0.1 to 0.8 MPa, and the treatment time is, for example, 15 minutes or more. [Example]

[0112] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. The specific numerical values ​​of the blending amounts (contents), physical properties, parameters, etc. described below can be substituted for the upper limits (numerical values ​​defined as "not more than" or "less than") or lower limits (numerical values ​​defined as "not less than" or "exceeding") of the corresponding blending amounts (contents), physical properties, parameters, etc. described in the above-mentioned "Description of the Invention."

[0113] Example 1 <Preparation of Prepolymer Composition> In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, a monomer mixture of 70 parts by weight of n-octyl acrylate, 20 parts by weight of n-butyl acrylate, 8 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 2 parts by weight of N-vinyl-2-pyrrolidone was added. 0.05 parts by weight of a photoinitiator (product name "Omnirad 184," 1-hydroxycyclohexyl phenyl ketone, IGM Resins) and 0.05 parts by weight of a second photoinitiator (product name "Omnirad 819," bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, IGM Resins) were then added. The mixture was then irradiated with UV light under a nitrogen atmosphere, polymerizing a portion of the monomer components in the mixture to obtain a prepolymer composition. A black light was used for UV irradiation. UV irradiation was continued until the viscosity of the prepolymer composition reached 10-20 Pa·s. The viscosity was measured using a Brookfield viscometer (product name "TVB-10M", manufactured by Toki Sangyo Co., Ltd.) with rotor No. 22, rotor rotation speed of 6 rpm, and temperature of 30°C. The obtained prepolymer composition was a partial polymer containing acrylic polymer P1 and unreacted monomer components (residual monomers). The weight-average molecular weight of acrylic polymer P1 in the prepolymer composition was approximately 4.3 million.

[0114] <Preparation of Oligomer> First, in a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, a mixture (solids concentration 26% by mass) containing 95 parts by mass of cyclohexyl methacrylate (CHMA), 5 parts by mass of acrylic acid (AA), 3 parts by mass of α-thioglycerol as a chain transfer agent, 0.3 parts by mass of azobisisobutyronitrile as a thermal polymerization initiator, and ethyl acetate as a solvent was reacted (polymerization reaction) at 72 to 74°C for 6 hours under a nitrogen atmosphere. Next, the reaction solution was heated at 90°C for 12 hours to volatilize and remove the ethyl acetate, chain transfer agent, and unreacted monomer. This yielded the solid oligomer used in Example 1. The glass transition temperatures of the oligomers used in Example 1 are shown in Table 1.

[0115] <Preparation of Pressure-Sensitive Adhesive Composition> To the prepolymer composition, 0.5 parts by mass of the oligomer, 0.11 parts by mass of dipentaerythritol hexaacrylate, 0.02 parts by mass of a photoinitiator (trade name "Omnirad 819", bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, manufactured by IGM Resins), and 0.5 parts by mass of a silane coupling agent (trade name "KBM-403", 3-glycidoxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) were added and mixed per 100 parts by mass of the monomer components (monomer components forming the base polymer) in the prepolymer composition to prepare a pressure-sensitive adhesive composition. The relative parts by mass of the oligomer per 100 parts by mass of the base polymer in the pressure-sensitive adhesive layer described below are shown in Table 1 as "blended amount (parts by mass)."

[0116] <Formation of adhesive layer> Next, a pressure-sensitive adhesive composition was applied to the release-treated surface of a first release liner (product name "Diafoil MRE#75", polyethylene terephthalate film, thickness 75 μm, manufactured by Mitsubishi Chemical Corporation), one side of which had been treated for silicone release, to form a coating film. Next, the release-treated surface of a second release liner (product name "Diafoil MRE#75", polyethylene terephthalate film, thickness 75 μm, manufactured by Mitsubishi Chemical Corporation), one side of which had been treated for silicone release, was bonded to the coating film on the first release liner. Next, the coating film between the release liners was irradiated with ultraviolet light, and this coating film was photocured to form a pressure-sensitive adhesive layer (thickness 50 μm). For ultraviolet irradiation, a black light was used as the irradiation light source, and the irradiation intensity was approximately 2.5 mW / cm. 2 The irradiation time was 16 minutes. In this manner, an optical pressure-sensitive adhesive sheet (thickness: 50 μm) with a release liner of Example 1 was produced.

[0117] Examples 2 to 4 and Comparative Examples 1 to 5 The oligomers used in each Example and Comparative Example were prepared in the same manner as the oligomer used in Example 1, except that the types and compositional ratios of the monomers used in preparing the oligomers were changed as shown in Table 1. DCPMA represents dicyclopentanyl methacrylate, MMA represents methyl methacrylate, MAA represents methacrylic acid, and HQMA represents hydroxyphenyl (meth)acrylate. The Tg of the oligomers used in each Example and Comparative Example is as shown in Table 1.

[0118] Furthermore, in preparing the pressure-sensitive adhesive composition, the optical pressure-sensitive adhesive sheets with release liner of Comparative Examples 1 to 5 were produced in the same manner as the optical pressure-sensitive adhesive sheet with release liner of Example 1, except that the type and amount of oligomer added was changed as shown in Table 1. Note that in Comparative Example 1, no oligomer was added.

[0119] <Evaluation> [Oligomer Tg] The Tg of the oligomers used in each Example and Comparative Example was calculated based on the Fox formula above, and the values ​​are shown in Table 1.

[0120] [HSP hydrogen bond term] The hydrogen bond term of the Hansen solubility parameter (HSP) was calculated for each of the base polymer and the oligomers used in each example and comparative example, and the difference (ΔH) between the base polymer and each oligomer was calculated. Specifically, it is as follows.

[0121] First, the hydrogen bond term of HSP was calculated for each monomer forming the oligomer using computer software HSPiP (Hansen Solubility Parameters in Practice). Next, the hydrogen bond term of the oligomer (δH2) was calculated from the molar fraction of the monomer in the oligomer and the hydrogen bond term of the monomer. For example, the hydrogen bond term of the oligomer used in Example 1 was calculated using the molar fraction of CHMA (molecular weight 154.2) of 0.8905 and the hydrogen bond term of 4.4 MPa. 1 / 2, the mole fraction of AA (molecular weight 72.1) is 0.1095 and the hydrogen bond term is 12.2 MPa 1 / 2 From 5.25 MPa 1 / 2 was asked.

[0122] Similarly, the hydrogen bond term (δH1) of the HSP of the base polymer was calculated. The value was 5.07 MPa. 1 / 2 The difference ΔH (= ΔH2 - ΔH1) between ΔH2 of the ligomer in the optical adhesive sheet and ΔH1 of the base polymer was calculated and is shown in Table 1.

[0123] [Shear storage modulus] The dynamic viscoelasticity of the optical pressure-sensitive adhesive sheets of each example and each comparative example was measured.

[0124] For each optical adhesive sheet, a measurement sample was prepared. Specifically, first, a plurality of optical adhesive sheet pieces cut out from the optical adhesive sheet were bonded together to prepare a sample sheet with a thickness of about 1.0 mm. Next, this sheet was punched to obtain a cylindrical pellet (diameter 7.9 mm) as a measurement sample.

[0125] Each of the prepared measurement samples was then fixed to a 7.9 mm diameter parallel plate jig using a dynamic viscoelasticity measuring device (product name: "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific) and subjected to dynamic viscoelasticity measurement. In this measurement, the measurement mode was shear mode, the measurement temperature range was -65°C to 200°C, the heating rate was 5°C / min, and the frequency was 1 Hz. The shear storage modulus at -30°C was read from the measurement results. The results are shown in Table 1.

[0126] [Adhesive strength] The adhesive strength of the optical pressure-sensitive adhesive sheets of each Example and Comparative Example to an adherend was measured by the following peel test.

[0127] (First peel test) A measurement sample was prepared for each optical adhesive sheet. Specifically, first, the first release liner was peeled from the optical adhesive sheet, and the exposed surface of the optical adhesive sheet was bonded to a plasma-treated polyethylene terephthalate film (product name "Lumirror S10", thickness 25 μm, manufactured by Toray Industries, Inc.) to obtain a laminate. The plasma treatment was performed using a plasma irradiation device (product name "AP-TO5", manufactured by Sekisui Kogyo Co., Ltd.) with a voltage of 160 V, a frequency of 10 kHz, and a treatment speed of 5000 mm / min. Next, a test piece (width 20 mm × length 100 mm) was cut from the laminate (PET film / optical adhesive sheet / second release liner). Next, the second release liner was peeled from the optical adhesive sheet of this test piece, and the exposed surface of the optical adhesive sheet was bonded to a glass plate (alkali glass, manufactured by Matsunami Glass Co., Ltd.). Next, the glass plate with the optical adhesive sheet (test piece) was heated and pressurized for 15 minutes at a temperature of 50°C and a pressure of 0.5 MPa. This caused the test piece to be pressure-bonded to the glass plate. In this way, a measurement sample was prepared.

[0128] Next, the test sample was left to stand at room temperature for 30 minutes, and then the test piece (polyethylene terephthalate film with optical adhesive sheet) was peeled from the glass plate, and the force required for peeling (peel strength) was measured. The measurement conditions were a temperature of 25°C, a relative humidity of 55%, a peel angle of 180°, a tensile speed of 300 mm / min, and a peel length of 50 mm. A tensile tester (product name "Autograph AG-50NX plus", manufactured by Shimadzu Corporation) was used for the measurement. The average measured peel strength is shown in Table 1 as adhesive strength F1 (N / 20 mm).

[0129] (Second peel test) The measurement conditions were the same as in the first peel test, except that the pulling speed was 60 mm / min. The average value of the measured peel strength is shown in Table 1 as adhesive strength F2 (N / 20 mm).

[0130] [Gel fraction] The gel fraction of the optical pressure-sensitive adhesive sheets of each example and each comparative example was measured as follows.

[0131] First, approximately 500 mg of a pressure-sensitive adhesive sample was collected from the optical pressure-sensitive adhesive sheet between the release liners. Next, the mass (W1) of the pressure-sensitive adhesive sample was measured. Next, the pressure-sensitive adhesive sample was immersed in approximately 40 g of ethyl acetate in a container for 7 days. Next, all components insoluble in ethyl acetate (insoluble portion) were collected. Next, the insoluble portion was dried at 130°C for 2 hours (removal of ethyl acetate). Next, the mass (W2) of the insoluble portion was measured. Then, the gel fraction (mass%) of the pressure-sensitive adhesive sheet after photocuring was calculated using the following formula. The values ​​are shown in Table 1.

[0132] Gel fraction (mass%) = (W2 / W1) × 100

[0133] [Hayes] The haze of the optical pressure-sensitive adhesive sheets of each example and each comparative example was measured as follows.

[0134] First, a sample for measurement was prepared. Specifically, the first release liner was peeled off from the optical pressure-sensitive adhesive sheet, and then the sheet was attached to alkali glass (thickness 1.0 mm, total light transmittance 92%, haze 0.4%, manufactured by Matsunami Glass Co., Ltd.). Next, the first release liner was peeled off from the optical pressure-sensitive adhesive sheet on the glass. This prepared a sample for measurement. Next, the haze of the optical pressure-sensitive adhesive sheet in the sample was measured using a haze meter (product name "HM-150", manufactured by Murakami Color Research Laboratory). The measurement was performed in accordance with JIS K7136 (2000). In this measurement, the sample was placed in the device so that light was irradiated from the alkali glass side of the sample. The measured haze is shown in Table 1.

[0135] [Table 1]

[0136] <Consideration> The optical pressure-sensitive adhesive sheets of Examples 1 to 4 have a shear storage modulus of 350 kPa or less at -30°C, are excellent in flexibility, and can alleviate stress generated in the optical pressure-sensitive adhesive sheet and adherend when used in flexible devices. On the other hand, the optical pressure-sensitive adhesive sheet of Comparative Example 3 has a shear storage modulus of more than 350 kPa at -30°C, is poor in flexibility, and is not suitable for flexible device applications.

[0137] In addition, in the optical adhesive sheets of Examples 1 to 4, the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, and the monomer component contains an acidic group-containing monomer, and the adhesive strength F1 (N / 20 mm) to glass in the first peel test satisfies 8.0≦F1. That is, the adhesiveness is excellent, and when used in a flexible device, peeling from the adherend can be suppressed. On the other hand, the optical adhesive sheet of Comparative Example 1 does not contain an oligomer, the optical adhesive sheet of Comparative Example 2 does not contain an oligomer, and the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, and the monomer component does not contain an acidic group-containing monomer, and the optical adhesive sheet of Comparative Example 4 does not contain an oligomer, and the monomer component contains an acidic group-containing monomer, but the adhesive strength F1 (N / 20 mm) to glass in the first peel test for the optical adhesive sheets of Comparative Examples 1, 2, and 4 is 8.0>F1. That is, the initial adhesiveness is poor and the adhesive is not suitable for flexible device applications. [Explanation of symbols]

[0138] 10 Optical adhesive sheet 11 1st adhesive side 12 Second adhesive side L1, L2 release liner 21 First member 22 Second member

Claims

1. An optical adhesive sheet comprising a base polymer and an oligomer, the oligomer is a polymer of a monomer component containing a (meth)acrylic acid ester monomer, the monomer component further includes an acidic group-containing monomer, The optical adhesive sheet has a shear storage modulus of 350 kPa or less at −30° C., An optical adhesive sheet whose adhesive strength F1 (N / 20 mm) to glass in the first peel test below satisfies the following formula (1). 8.0≦F1 (1) (First Peel Test) A polyethylene terephthalate film is attached to one side of the optical adhesive sheet, and the other side is attached to a glass plate, followed by heating and pressurizing to prepare a measurement sample. After leaving the measurement sample at room temperature for 30 minutes, the test piece (the polyethylene terephthalate film with the optical adhesive sheet) is peeled from the glass plate. The measurement conditions are as follows: temperature 25 ° C, relative humidity 55%, peel angle of the test piece from the glass plate 180 °, tensile speed 300 mm / min, peel length 50 mm.

2. The optical pressure-sensitive adhesive sheet according to claim 1, wherein the adhesive strength F2 (N / 20 mm) to glass in the second peel test below satisfies the following formula (2). 6.0≦F2 (2) (Second Peel Test) The measurement conditions are the same as those of the first peel test, except that the pulling speed is 60 mm / min.

3. The optical adhesive sheet according to claim 1 , wherein the (meth)acrylic acid ester monomer further comprises an alicyclic alkyl group-containing (meth)acrylic acid ester monomer.

4. The optical adhesive sheet according to claim 1 , wherein in the acidic group-containing monomer, the acidic group is a carboxy group and / or a phenolic hydroxy group.

5. The optical adhesive sheet according to claim 1, wherein the homopolymer of the acidic group-containing monomer has a glass transition temperature of 40°C or higher.

6. The optical adhesive sheet according to any one of claims 1 to 5, wherein the content of the acidic group-containing monomer in the monomer component is 1 mass% or more and 20 mass% or less.

7. The optical adhesive sheet according to any one of claims 1 to 5, wherein the amount of the oligomer blended is 0.3 parts by mass or more and less than 1.5 parts by mass relative to 100 parts by mass of the base polymer.

8. The optical pressure-sensitive adhesive sheet according to any one of claims 1 to 5, having a haze of 1% or less.

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